Materials with anisotropic electrical properties are of significant interest in the electronic warfare community. Such materials find utility in defending aircraft and related vehicles from electronic discovery as a result of their ability to achieve oppositely signed index of refraction characteristics. These “negative index” materials also have the potential to create cheaper, lighter, and more simplistic phased array radar systems for example. Most materials of these characteristics are in fact man-made and may be based on such fabricated arrangements as dispersion of split ring resonator and thin wire “post elements” into a composite material. The resulting material has negative permeability from the split ring resonators and negative permittivity from the post elements within a specifically designed passband and is thus considered a negative index material. Otherwise the material has positive permeability and permittivity characteristics in lieu of “anisotropic characteristics” attending negative index materials.
Materials of this nature are thusly of current importance in the more fundamental and research oriented work of the electronic community. It has been found however that the laboratory apparatus used to characterize positive index electromagnetic materials are not well suited to characterize the anisotropic nature of positive or negative index materials. A part of this difficulty may be attributed to measurements involving the physical disposition of transducers into physical locations, with respect to a sample, that are simply different from the locations needed for isotropic positive index materials. More subtle however is the fact that the signals emitted from samples of anisotropic positive and the unique properties of negative index materials can be so different from anisotropic positive materials as to be susceptible to being totally missed or ignored during an investigation without the use of enhanced measuring apparatus. This is the area of concern in the present invention.
Horn antennas may be used to focus radiated electrical energy on-to and through a tested material sample in order to discern certain such electrical properties of the sample. The underlying purpose of focusing an electrical energy beam in this way is for example to measure electrical reflection and transmission properties of the material—preferably in a manner that is more easily accomplished as compared to such traditional near field techniques as anechoic chamber measurements. Such traditional near field anechoic chamber measurements often for example dissipate or absorb a reflected wave from a sample under test. With focusing horn antennas, such near field data is readily available, typically allowing for effective permeability and permittivity characteristics to be determined over a broad range of measuring frequencies.
A spot focusing horn lens antenna measurement system may be achieved through manually adjusting the distance between energy transducer horns and the sample material in order to maximize effects of the transmitted and received electrical energy. In previous such system configurations, in order to make off-axis energy measurements, either the horn or the material sample require manual adjustment in order to achieve desirable measuring accuracy.
A primary focus of the present invention is to automate a horn antenna based material characterization process, as well as provide further measurement capabilities in characterizing anisotropy and antenna polarization rotation measurements.